The colours observed in thin soap bubbles are due to

White light is incident at an angle of $30^\circ$ on a soap film with a refractive index of $4/3$. The wavelength of the transmitted light is observed to be $6 \times 10^{-5} \, cm$. Find the minimum thickness of the film.

If Fresnel's biprism experiment is performed in water instead of air,what will be the effect on the fringe width?

In a biprism experiment,the distance of the second dark fringe from the central fringe is $3 \ mm$. The distance of the sixth bright fringe from the central fringe is (in $mm$)

In a biprism experiment,if the $5^{\text{th}}$ bright band with wavelength $\lambda_1$ coincides with the $6^{\text{th}}$ dark band with wavelength $\lambda_2$,then the ratio $(\lambda_1 / \lambda_2)$ is:

$A$ light of wavelength $5890 \; \mathring{A}$ falls normally on a thin air film. What is the minimum thickness of the film such that the film appears dark in reflected light?